Trombicula, commonly known as chiggers, are tiny mites that cause intensely itchy bites. These microscopic relatives of spiders and ticks are also called harvest mites, red bugs, or scrub-itch mites. Though small, their presence often becomes clear due to the irritating skin reactions they trigger, a common summertime nuisance in many regions.
Understanding Chiggers
Chiggers belong to the family Trombiculidae. Only their six-legged larval stage is parasitic, feeding on humans and animals. The subsequent nymph and adult stages are free-living, eight-legged predators that inhabit the soil and consume small arthropods and their eggs.
These mites are often found in outdoor environments with heavy vegetation, such as grassy fields or wooded areas, particularly in moist conditions. They are most active in early summer in temperate regions, with activity peaking when ground temperatures range from approximately 77 to 86 degrees Fahrenheit. Chiggers are not host-specific and feed on various vertebrates, including humans, birds, and reptiles.
How Chiggers Bite and Their Effects
When a larval chigger encounters a host, it attaches to skin, often where clothing fits tightly, such as waistbands, sock lines, or skin folds. Unlike ticks or mosquitoes, chiggers do not burrow into the skin or suck blood. Instead, they use specialized mouthparts to pierce the skin and inject digestive enzymes.
These enzymes break down skin cells, creating a hardened, straw-like feeding tube called a stylostome. The body’s immune reaction to the chigger’s saliva and stylostome causes symptoms, which begin hours after exposure. This reaction manifests as intense itching, which can be severe and persist for days to two weeks. Red welts, bumps, or sometimes blisters and hives may appear at the bite sites.
Preventing and Treating Chigger Bites
Preventing chigger bites involves minimizing exposure and using protective measures. When outdoors in grassy or wooded areas, wear long sleeves, long pants, and tuck pant legs into socks or boots to reduce skin exposure. Apply insect repellents containing DEET, picaridin, or oil of lemon eucalyptus to exposed skin.
For clothing, treating it with permethrin, an insecticide, provides additional protection as it kills chiggers on contact. Apply permethrin to clothing in advance and allow it to dry before wearing. After spending time outdoors, shower promptly with soap and water to dislodge any attached chiggers, preventing them from feeding. Also wash exposed clothing in hot, soapy water to eliminate any remaining mites.
If bites occur, treatment aims to relieve itching and prevent secondary infections. Over-the-counter anti-itch creams like calamine lotion or hydrocortisone cream (1%) can be applied, and oral antihistamines, such as diphenhydramine or cetirizine, can also help manage widespread itching. A cold compress or cool bath may further reduce discomfort. Avoid scratching bites to prevent breaking the skin, which can lead to bacterial infections. If signs of infection develop (e.g., increased redness, warmth, swelling, pus), seek medical attention.
Beyond the Itch: Other Health Considerations
While chigger bites in North America cause intense itching and localized skin reactions, certain Trombicula species in other parts of the world can transmit serious diseases. For instance, species like Leptotrombidium deliense and Trombicula akamushi in the Asia-Pacific region transmit scrub typhus. This bacterial infection, caused by Orientia tsutsugamushi, can affect over 1 million people annually.
Symptoms of scrub typhus appear 6 to 21 days after a bite and can include fever, chills, headache, muscle pain, and swollen lymph nodes. A characteristic black, crusted lesion (eschar) may also develop at the bite site. If untreated, scrub typhus can lead to severe complications like pneumonia, meningitis, and organ failure, with a significant mortality rate. Beyond specific diseases, any chigger bite carries a risk of secondary bacterial infections if the skin is broken by scratching.